Method of navigating a vehicle with an electronic device using bilateration

ABSTRACT

A method of navigating a vehicle with an electronic device using bilateration to a desired location is disclosed. The method includes the steps of receiving, with an electronic device, a plurality of signals emitted from a plurality of transmitting devices within a vicinity of the electronic device and determining a signal quality for the signals that are received based on 1) a RSSI or 2) a received signal power and a received signal gain, and signal propagation characteristics based on transmitting device information. The signal propagation characteristics is compared with either 1) the RSSI or 2) the received signal power and the received signal gain and at least two of the signals are designated having a highest signal quality, and are used to determine a distance that the electronic device is from the transmitting devices for locating the electronic device. New coordinates are generated for the electronic device based upon the distances from the plurality of transmitting devices and the new coordinates are recorded as a current location of the electronic device to thereby navigate the vehicle. The current location of the vehicle is compared to the desired location and new coordinates continue generating as the vehicle moves.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No. 17/181,307filed on Feb. 22, 20201 which is a continuation application of U.S.application Ser. No. 16/934,436 filed on Jul. 21, 2020, now U.S. Pat.No. 10,966,060 which is a continuation application of U.S. applicationSer. No. 16/000,530 filed on Jun. 5, 2018, now U.S. Pat. No. 10,743,141.

BACKGROUND 1. Field of the Invention

The subject invention relates to a method for determining a location ofan electronic device using bilateration.

2. Description of Related Art

As electronic devices, such as computers and cell phones, have becomemore prevalent, there is a growing desire to determine the location forsuch devices for a variety of applications. One of the most prevalentconsumer applications has been in travel. The electronic device mayreside in an unknown location, and it may be desirable to determine thelocation of the device. One common approach is to use a GlobalPositioning System (“GPS”) to determine location. GPS systemsincorporate navigation systems which help the user find their desireddestinations. Many of the systems provide navigation with visual andaudio cues that aid the user in navigating through streets and highwayswhich may be unfamiliar to the user.

However, GPS systems require line-of-sight signals from GPS satellites,so in cities, the presence of tall buildings can make it difficult toreceive an accurate GPS signal. Tall buildings create what is referredto as an urban canyon environment. The presence of buildings andlandscaping can block the open sky from view by a GPS receiver.Reflections can also degrade GPS signals by causing multipathinterference. As a result, GPS location information can be slow orimpossible to obtain. Further, in situations such as those involvingroads with branches, GPS systems in vehicles can have difficulties inaccurately determining which branch of the road a vehicle is located on.As a result, commercially available GPS solutions may not providesufficient resolution to determine when a vehicle has exited a freeway.In large cities such as San Francisco, New York, and Chicago, there aremany locations in which GPS signals do not operate or may not providesufficiently consistent location data for navigation. For example, if auser takes the subway around the city, the current GPS systems may notbe able to determine any locations within the tunnels, and this may leada user to exit the train at the wrong train station. Also, manydestinations in a large metropolitan city may require a verticalcoordinate as well as a longitudinal and latitudinal coordinate. Forexample, a store within a mall may be located on the top level of abuilding.

To address the problems associated with using GPS signals to ascertain auser's location in an urban canyon environment, some electronic devicesrely on triangulation from signals of nearby cellular telephone towersor information about nearby Wi-Fi hotspots. However, such known systemsrequire at least three signals and can consume additional time if manysignals are present. Further, the known methodologies do not providesufficiently consistent and accurate location data for the electronicdevice. This is most prevalent in the urban canyon environment when thelocation is displayed on a mapping program and the location skips orjumps about the map as different signals are received.

SUMMARY

The subject invention provides a method of navigating a vehicle with anelectronic device using bilateration to a desired location. The methodcomprises the steps of receiving, with the electronic device, aplurality of signals emitted from a plurality of transmitting deviceswithin a vicinity of the electronic device. A signal quality isdetermined for the plurality of signals that are received based on 1) areceived signal strength indicator or 2) a received signal power and areceived signal gain, and signal propagation characteristics based ontransmitting device information that comprises manufacturer and type oftransmitting device for each of the plurality of transmitting devices.The signal propagation characteristics are compared with either 1) thereceived signal strength indicator or 2) the received signal power andthe received signal gain and two of the plurality of signals aredesignated having highest signal quality for location determination. Adistance that the electronic device is from the transmitting devices isdetermined using the two highest signal quality signals for locating theelectronic device. New coordinates for the electronic device aregenerated based upon the distances from the plurality of transmittingdevices and the new coordinates are recorded as a current location ofthe electronic device to thereby navigate the vehicle. The currentlocation of the vehicle is compared to the desired location and newcoordinates continue to be generated as the vehicle moves.

The systems and methods described herein address how to mitigate variousproblems associated with local-area-network-assisted locationdetermination (e.g., Wi-Fi assisted location determination) and produceconsistently accurate and precise locations. The subject invention canproduce precise location determinations for the electronic device from10 times to 100 times a second. Further, the location determinationsperformed according to the subject invention are able to be accuratewithin a few feet, even in environments such as urban canyons. Moreover,the subject invention provides accurate location determinations even ifthere are only two signals available.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an electronic device spaced from transmitting devices anda location of the electronic device is determined using bilateration;

FIG. 2 is a schematic view of an electronic device;

FIG. 3 is a schematic view of an environment using the subject inventionhaving a plurality of vehicles traveling on a road through a city;

FIG. 4 is a process flow diagram showing one method of obtaining a firstlocation from a cellular network input using time of flight and angle ofincoming signal;

FIG. 5 is a schematic view of an environment using the subject inventionhaving a plurality of vehicles traveling on a road;

FIGS. 6A and 6B show illustrative transmission circles for transmittingdevices and an electronic device is at one of the two intersections ofthe circles;

FIG. 7A-7D are graphical displays of a mapping program having thelocation of an electronic device plotted thereon;

FIG. 8 is a process flow diagram showing another method to determine alocation of an electronic device;

FIGS. 9A and 9B are process flow diagrams showing yet another example ofa method that can be performed to determine a location of the electronicdevice;

FIG. 10 is a process flow diagram for still another method than can beperformed to determine a location of the electronic device;

FIG. 11 is a process flow diagram for a method of determining a state ofa virtual accelerometer; and

FIG. 12 is a process flow diagram for another method of determining astate of a virtual accelerometer.

DETAILED DESCRIPTION

Referring to the Figures, wherein like numerals indicate like orcorresponding parts or steps throughout the several views, FIG. 1depicts an electronic device, shown generally at 10, spaced fromtransmitting devices, shown generally at 12, and a location of theelectronic device 10 is determined using bilateration. The method isable to determine the location of the electronic device 10 viageolocation identification in mobile Heterogeneous Networks (HetNet)environments. In some embodiments, the electronic device 10 may haveconnectivity to a transmitting device 12. Here, “connectivity” does notnecessarily require that a wireless session be initiated between thetransmitting device 12 and the electronic device 10; instead, it may besufficient that data (e.g., IP/WLAN packets) can be successfullytransmitted from the electronic device 10 to the transmitting device 12,or from the transmitting device 12 to the electronic device 10. Forexample, if the electronic device 10 is scanning for wireless networksand is able to detect a service set identifier (SSID) associated with awireless local-area network facilitated by the transmitting device 12,the electronic device 10 and the transmitting device 12 may be said tohave connectivity to each other. In such examples, the SSID may be usedto generate the transmitting device 12 connectivity notification.

Each of the components in the system according to the invention havebidirectional wireless capabilities (e.g., to support the transmissionand receipt of signals using well known and standard protocols). In FIG.1, the electronic device 10 may be sending and receiving the signals andthe transmitting devices 12 may also be sending and receiving thesignals. Each signal may include location information of thetransmitting devices 12, as will be discussed below. In one embodiment,the electronic device 10 having the unknown location receives signalstransmitted from transmitting devices 12 to determine the unknownlocation. In other embodiments, the electronic device 10 having theunknown location transmits one or more signals, which are received bytransmitting devices 12 to determine the unknown location. Some or allof the devices may both transmit and receive to improve the accuracy ofthe distance measurement. This provides more data to process and theaveraging that results from processing more information improves theaccuracy of the distance measurement since the effect of random errorsis reduced. In certain embodiments, the electronic device 10 mayinstruct the transmitting devices 12 within the vicinity of theelectronic device 10 to transmit a signal, and the signal may includesuch location information. As one example, the electronic device 10 mayuse an Access Network Query Protocol (ANQP) for Wi-Fi Hotspot 2.0 basedon the IEEE 802.11u standard. Other protocols and procedures used inWi-Fi technology to identify wireless SSIDs may be utilized for thequery without deviating from the subject invention.

Referring to FIG. 2, by way of example, the electronic device 10 mayinclude one or more radio-frequency transceivers 14, cellular telephonetransceivers 16, IEEE 802.11 (Wi-Fi) transceivers 18 (e.g., one or morewireless local area network transmitting devices and/or receivers),Bluetooth transceivers 20, and satellite navigation system receivercircuitry 22 (e.g., a Global Positioning System receiver or othersatellite navigation system receiver). It is to be appreciated thatvarious configurations and combinations of such circuity may be usedwith the electronic device 10 according to the subject invention, whilestill practicing the invention.

The electronic device 10 also includes an antenna 24 connected thereto.In certain embodiments, the antenna 24 may be a tunable antenna, whichmay also be referred to as a reconfigurable antenna or aself-structuring antenna. The tunable antenna 24 is capable of modifyingdynamically its frequency properties in a controlled and reversiblemanner. It is to be appreciated that multiple antennas, each for adifferent frequency type, could be used in place of the tunable antenna24 without deviating from the subject invention so long the electronicdevice 10 is able to switch between antennas to tune for a specificsignal type and frequency. One type of self-structuring antenna 24 maybe obtained from Monarch Antenna, Inc. The tuning of the antenna 24 mayalso be performed with software.

As shown in FIG. 2, the electronic device 10 may also include controlcircuitry such as storage and processing circuitry. Storage andprocessing circuitry may include one or more different types of storagesuch as hard disk drive storage 26 and memory 28. The memory may benon-volatile (e.g., flash memory or otherelectrically-programmable-read-only memory) or volatile memory (e.g.,static or dynamic random-access-memory). Processing circuitry may beused in controlling the operation of electronic device 10. Theprocessing circuitry may be based on a processor 30 such as amicroprocessor and other suitable integrated circuits. With one suitablearrangement, the storage and processing circuitry may be used to runsoftware on the electronic device 10, such as mapping applications(e.g., navigation applications for a vehicle 40 or electronic device10), email applications, media playback applications, operating systemfunctions, software for capturing and processing images, softwareimplementing functions associated with gathering and processing sensordata, software for issuing alerts and taking other actions when suitablecriteria are satisfied, software that makes adjustments to displaybrightness and touch sensor functionality, etc. The operation of thestorage and processing circuitry is well known to those of ordinaryskill in the art, and the specifics details of such operation is notnecessary for an understanding of the subject invention and is thereforenot included.

Input-output circuitry may be used to allow data to be supplied to theelectronic device 10 and to allow data to be provided from theelectronic device 10 to external devices. Input-output circuitry 32 mayinclude, by way of example and not limitation, input-output devices suchas buttons, joysticks, click wheels, scrolling wheels, touch screens,other components with touch sensors such as track pads ortouch-sensor-based buttons, vibrators, audio components such asmicrophones and speakers, image capture devices such as a camera modulehaving an image sensor and a corresponding lens system, keyboards,status-indicator lights, tone generators, key pads, keyboards and otherequipment for gathering input from a user or other external sourceand/or generating output for a user.

The electronic device 10 may also include sensor circuitry, such as, butnot limited to, a gyroscope 34, a compass 36, an accelerometer 38, andother sensors for gathering data for the electronic device 10.

The electronic device 10 may be a cellular telephone, tablet computer orother portable computer, embedded equipment in a vehicle 40, or othermobile electronic equipment. Referring to FIG. 3, one example of anenvironment using the subject invention is shown having a plurality ofvehicles 40 traveling on a road through a city. Each of the vehicles 40may include a transmitting device 12 or an electronic device 10 or both.Buildings 42 are located adjacent the road and each of the building 42may have one or more transmitting devices 12. Other structures, such aslight posts 44 may be adjacent the road and may have transmittingdevices 12 mounted thereto. In such an environment, the types of signalsbeing transmitted have various, different signal types and the variousobjects may impact and/or interfere with the strength of such signals.The building 42 and other structures may be located adjacent to roadsand create urban canyon environments. In such urban canyon environments,it may be challenging for electronic equipment, such as vehicle 40, toobtain accurate location information using only satellite navigationequipment, so according to the invention, the vehicle 40 may communicatewith other transmitting devices 12 to more accurately and preciselydetermine location.

Referring back to FIG. 1, a plurality of transmitting devices 12 areshown in the vicinity of the electronic device 10. The electronic device10 is at a first, or initial location that can be represented bycoordinates. It is to be appreciated that the method repeats many timesa second such that the initial location can also be a previous locationor the most previous location from the prior cycle. The first locationcan be obtained from a vehicle 40 input, a GPS input, or a cellularnetwork input or it can be determined based on trilateration of at leastthree or more of known Wi-Fi hotspot locations and signal strength, GPSinput, or cellular network input. The first location could also becalculated from the data on the electronic device 10. Referring to FIG.4, a process flow is shown for one method of obtaining the firstlocation from a cellular network input using time of flight and angle ofincoming signal, which are well known. The first location may becompared to a topographic map to determine the first location. Thecoordinate location may also be represented by at least 16 decimalplaces.

As shown in FIG. 1, the transmitting devices 12 are located at specificcoordinates. The coordinates are represented by an X-coordinate and aY-coordinate. It is to be appreciated that a Z-coordinate could also beincluded. Each of the transmitting devices 12 are a distance from theelectronic device 10, which is represented by D1, D2, etc. Thetransmitting device 12 may be stationary transmitting device 12 attachedto the interior or exterior of a building 42, mounted alongside aroadway, mounted in a traffic light or traffic sign, or otherwiseinstalled in a stationary location. The transmitting device 12 may alsobe a mobile location, when incorporated into vehicles 40, trains, or thelike.

The transmitting device 12 may include, but is not limited to, acomputer, router, switch, hub, universal serial bus (USB) stick,roadside units 46 (RSU), or any other device capable of receiving andtransmitting data (e.g., Internet Protocol (IP) packets, wirelesslocal-area network (WLAN) packets, etc.) or any other device thattransmits signals that are connected to a Wide Area Network (WAN). Thetransmitting devices 12 can include WLAN operating at differentfrequencies and using several wireless standards.

The transmitting devices 12 are transmitting signals, or messages, thatare received by the electronic device 10. The type of signals that arebeing transmitted can vary widely, but may include Wi-Fi signals,cellular signals, Wireless Access in Vehicular Environment (WAVE)signals, and GPS signals. The Wi-Fi signals can include, but are notlimited to IEEE 802.11a, b, g, n, signals. The cellular signals caninclude, but are not limited to global system for mobile communications(GSM), code division multiple access (CDMA), General Packet RadioService (GPRS), 4G, 5G. Other communication protocols can also besupported, including other 802.11x communication protocols (e.g.,WiMax,), Enhanced Data GSM Environment (EDGE), etc.

The WAVE signal supports communication of fast running vehicles, and isconfigured with the Institute of Electrical and Electronics Engineers(IEEE) 802.11p and the IEEE 1609, generally in the 5.9 Ghz spectrum. TheIEEE 1609.3 of the IEEE 1609 defines a network layer and a transportlayer service, and the IEEE 1609.4 provides a multichannel operation. Totake advantage of WAVE, the vehicle 40 has an onboard unit (OBU) andcommunicates with the RSU 46. RSUs 46 may be installed on both sides ofthe road and at various locations along the roadway. In such a system,the OBU may operate as the electronic device 10, the transmitting device12, or both depending on the particular location or application. Whenvehicle to vehicle (V2V) communication is established, one OBU is theelectronic device 10, while the other is the transmitting device 12 orvice versa. When vehicle 40 to infrastructure (V2I) communication isestablished, the OBU is the electronic device 10 and is communicatingwith the RSU 46 as the transmitting device 12. RSUs 46 have anestablished location that is precisely known. Referring to FIG. 5, twoRSUs 46 are shown adjacent the road communicating with the OBU of thevehicle 40 as the electronic device 10.

For stationary transmitting devices 12, the location information may beknown and transmitted as part of the signal or available from publicWi-Fi location databases, such as SkyHook Wireless, Combain PositioningService, LocationAPI.org by Unwired Labs, Mozilla Location Service,Mylnikov GEO, Navizon, WiGLE, amongst others. The location informationcan include latitude, longitude, altitude, as well the transmittingdevice 12 model number, manufacturer name, model/device name or type,owner name, etc.

The transmitting device 12 may be able to store transmitting devicelocation coordinates. For example, the transmitting device locationcoordinates may be stored in a location configuration information (LCI)format which may include, without limitation, latitude, longitude,and/or altitude information. As another example, the transmitting devicelocation coordinates may be stored in a civic format which may include,without limitation, door number, street address, suite number, city,state, country, zip code, etc. The location coordinates may be storedlocally on the electronic device 10 or stored remotely so that theelectronic device 10 may access it.

In yet another embodiment, the transmitting device 12 can transmit morethan once where each signal has a different center frequency and theelectronic device 10 can receive and handle these differenttransmissions. For example, 802.11a and 802.11b use two differentfrequencies and if both the transmitting device 12 and electronic device10 support 802.11a and 802.11b then using both provides betteraveraging. Yet another embodiment is for the transmitting device 12 totransmit more than once where each signal uses a different wirelessstandard, such as WLAN and UWB. The electronic device 10 supports thesedifferent wireless standards and more data is gathered and locationaccuracy is improved through averaging. The electronic device 10 mayalso receive a signal from the cellular network tower. The cellcommunication can include, for example, information identifying the celltower. In some implementations, the cell communication can also includethe latitude and longitude of the cell tower.

The method according to the subject invention comprises the step ofobtaining a first location comprising coordinates of the electronicdevice 10. Referring again to FIG. 1, the electronic device 10 receivesa plurality of signals emitted from transmitting devices 12 within avicinity of the electronic device 10 with the antenna 24. Each of thetransmitting devices 12 may be transmitting the same or different signaltypes. A signal quality is determined for a first signal transmittedfrom a first transmitting device 12 a having a first signal type basedon: 1) a received signal strength indicator (RSSI) or a received signalpower and a received signal gain for the first signal, and 2) signalpropagation characteristics for the first transmitting device 12 a. Itis to be appreciated that the electronic device 10 may simultaneouslyreceive the plurality of signals and may simultaneously or nearlysimultaneously determine the signal quality for more than one signal.

The RSSI that is received may be provided as part of the signal andrepresents a measurement of the power present in the received signal.The RSSI is the relative signal strength and is typically in arbitraryunits, whereas power is typically measured in decibels. If the RSSI isnot provided, the electronic device 10 may calculate the signal strengthbased on the received signal power and the received signal gain for thefirst signal or both. The electronic device 10 may use the storage andprocessing circuitry or other circuitry to determine the signal strengthfrom the power and gain of the received first signal. Typically, whenthe electronic device 10 is located a certain distance from thetransmitting device 12, the signal will have a certain RSSI or signalstrength. The RSSI or signal strength fluctuates even though theelectronic device 10 remains in the same location as a result ofnumerous issues. Alternatively, the received channel power indicator(RCPI) may be received.

In order to determine the signal quality, the electronic device 10 doesnot merely rely on RSSI or signal strength, but also uses the signalpropagation characteristics associated with the first transmittingdevice 12 a. The signal from the first transmitting device 12 a mayinclude the manufacturer of the device and the type of device or thisinformation is retrievable based on the signal. A device database isqueried based on manufacturer and type of the first transmitting device12 a to determine the actual signal propagation characteristics. Thedevice database may be stored locally on the electronic device 10 orstored remotely so that the electronic device 10 may access it. From thedevice database, the signal propagation curve can be obtained andcompared with the RSSI to determine whether the signal is of sufficientquality. Because the RSSI or signal strength fluctuates or wavers, theidentification of the highest quality signal can be skewed. By combiningthe RSSI or signal strength with the signal propagation characteristics,the electronic device 10 can control how the signal is received and canpredict the fluctuations, which results in a more stable detection andhigher signal quality.

Next, the first signal having the highest signal quality is designatedfor location determination. The signals may be used for a set timeperiod, such as 2 seconds, before scanning for other higher qualitysignals. The antenna 24 is tuned for the first signal type and the firstsignal is received with the tuned antenna 24. The first signal receivedwith the tuned antenna 24 is used to determine a distance D1 from thefirst transmitting device 12 a. The distance can be determined based onone or more of: a received signal power and a received signal gain forthe first signal as received by the tuned antenna 24, at least one oftransmitted power and transmitted signal gain of the first signal forthe first transmitting device 12 a, or location information associatedwith the first transmitting device 12 a identified by at least one of amedia access control (MAC) address and an internet protocol (IP)address. It is to be appreciated that the term “one or more” does notrequire one of each of the elements to be present. For example, thedistance may be determined by only the received signal power and thereceived signal gain or by only the transmitted power and transmittedsignal gain of the first signal for the first transmitting device 12 a,if possible. Alternatively, the distance may be determined based only onthe location information associated with the first transmitting device12 a. Or, the distance could be determined based on a combination ofeach.

The location information of the transmitting device 12 may include theSSID and the MAC address of the transmitting device 12. From the SSID orthe MAC address, a signal strength for the first signal may be receivedat the electronic device 10 based on the first transmitting device 12 a.The signal strength may be, for example, measured in Watts, Volts, dBm,dB, or like units. As discussed above, the signal strength can be RSSIor calculated from the power and gain. The accuracy of the locationinformation may depend on the number of positions that have been enteredinto the database and on which databases are used.

One approach for determining the distance is determined according to thefollowing formula:

d=10 {circumflex over ( )} [log₁₀(λ)−(P _(r) −P _(t) −G _(t) −G_(r))/20−log₁₀(4 π)];

where d is distance in meters; λ is the wavelength of the signal inmeters, P_(r) is the power of the received signal in decibels, P_(t) isthe power of the transmitted signal in decibels, G_(t) is the gain ofthe transmitted signal in decibels, and G_(r) is the gain of thereceived signal in decibels.

Another approach to determining the distance is determined according tothe following formula:

d=10 {circumflex over ( )} ((27.55−(20.0*10 {circumflex over ( )} v)+|RSSI |)/20)+45

where d is distance in meters; v is the frequency of the signal in MHz,and RSSI is received signal strength by the electronic device 10.

Next, a signal quality for a second signal is determined from a secondtransmitting device 12 b. It is to be appreciated that the first and thesecond signals may be received simultaneously or near simultaneously.The subject invention may receive the signals 10 to 100 times a secondand, as such, the determinations may be performed 10 times a second andup to 100 times a second. As faster data processing speeds are possible,the subject invention may process up to 1000 times a second if moreaccuracy is desired. The second signal may have a second signal typedifferent than or the same as the first signal. The signal quality isbased on the same factors used from the first signal, as discussed aboveand applied to the second signal. The second signal having the nexthighest signal quality is designated for location determination. Inother words, the method will use the second signal with next highestsignal quality.

The antenna 24 is tuned for the second signal type and the second signalis received with the tuned antenna 24. A distance is determined from thesecond transmitting device 12 b based on one or more of: a receivedsignal power and a received signal gain for the second signal asreceived by the tuned antenna 24, transmitted power and transmittedsignal gain of the second signal for the second transmitting device 12b, or location information associated with the second transmittingdevice 12 b identified by at least one of a media access control (MAC)address and an internet protocol (IP) address. Determining the distanceof the electronic device 10 from the second transmitting device 12 busing the tuned antenna 24 is the same as described above with respectto the first transmitting device 12 a. However, it is to be appreciatedthat determining the distance from the first and second transmittingdevices 12 a, 12 b may be different and may rely on different variablesbetween the first and second signals.

Once the distances of the first and second transmitting devices 12 a, 12b are known from the respective first and second signals, the relativelocation between the electronic device 10 and the respective first andsecond transmitting devices 12 is ascertained and first and secondtransmission circles are developed based upon the distances. Next, thepoints of intersection are determined where the first and secondtransmission circles intersect.

FIG. 6A shows illustrative transmission circles for the transmittingdevices and the electronic device 10 is at one of the two intersectionsof the circles. The location coordinate for the electronic device 10 canbe narrowed down to one of two intersection coordinates, (X0, Y0) and(X0′, Y0′), which are the points of intersection of circles C1 and C2defined by using the location coordinates (X1, Y1) and (X2, Y2) ascenters of the circles C1 and C2, respectively, and device distances D1and D2 as radii of the circles C1 and C2, respectively. The firsttransmitting device 12 a is at location coordinates (X1, Y1) and thesecond transmitting device 12 b is at location coordinates (X2, Y2). Theelectronic device 10 is a distance D1 from the first transmitting device12 a and a distance D2 from the second transmitting device 12 b. In thisexample, each location is defined in terms of two-dimensional Cartesiancoordinates (X and Y). However, it is to be understood that any spatiallocation coordinate system may be used with dimensionality ranging froma single dimension (e.g., (X); (θ); etc.) to three dimensions (e.g., (X,Y, Z); (R, θ, (φ); etc.). The Z coordinate in the X, Y, Z coordinatesmay correspond to the vertical location (height) of the transmittingdevices 12. Transmitting devices 12 may be positioned at each level in amultilevel roadway, the electronic device 10 may be provided withinformation on which level vehicle 40 is located on (either frominformation such as a transmitted Z location from transmitting devices12 or transmitted roadway level information).

Referring to FIG. 6B, the two circles are shown on a graph withCartesian coordinates. The distance between the centers of C1 and C2 is:

D _(C1−C2)=√{square root over ((X2−X1)²+(Y2−Y1)²)}

The equation for the line connecting the two intersection positions is:

$y = {{\frac{{X1} - {X2}}{{Y2} - {Y1}}x} + \frac{\left( {{D1^{2}} - {D2^{2}}} \right) + \left( {{X2^{2}} - {X1^{2}}} \right) + \left( {{Y2^{2}} - {Y1^{2}}} \right)}{2\left( {{Y2} - {Y1}} \right)}}$

Since the electronic device 10 may be located at either of the two pointof intersection, the method determines which of the two points ofintersection is reliable. In order to determine which intersection isreliable, the intersection coordinates are compared to the first (orprevious) location coordinates to determine if the intersectioncoordinates are feasible. This is based on detecting movement of theelectronic device 10 to a subsequent location from the first location.The movement may include velocity and direction, which are provided byat least one or more of the accelerometer 38 or the gyroscope 34. Forexample, if the current direction of the electronic device 10 is known,then the current direction can be compared to the intersectioncoordinates to determine if either are reliable and/or if one is morereliable than the other. The following equations are useful indetermining the intersection coordinate distance from a previousintersection coordinate:

${{\left. 1 \right)\mspace{14mu}{Latitude}\mspace{14mu}{Difference}\mspace{14mu}\left( {{in}\mspace{14mu}{radians}} \right)} = {{\left( \frac{\pi}{180} \right)*\left( {{Latitude}\mspace{14mu} 2} \right)} - \left( {{Latitude}\mspace{14mu} 1} \right)}};$

where Latitude 2 is the latitude at the current location and Latitude 1is the latitude at the previous location.

${{\left. 2 \right)\mspace{14mu}{Longitude}\mspace{14mu}{Difference}\mspace{14mu}\left( {{in}\mspace{14mu}{radians}} \right)} = {{\left( \frac{\pi}{180} \right)*\left( {{Longitude}\mspace{14mu} 1} \right)} - \left( {{Longitude}\mspace{14mu} 2} \right)}};$

where Longitude 2 is the longitude at the current location and Longitude1 is the longitude at the previous location.

${\left. {{\left. {{\left. {{\left. {{\left. \mspace{20mu} 3 \right)\mspace{14mu}{Latitude}\mspace{14mu} 1\mspace{14mu}{radians}} = {\left( \frac{\pi}{180} \right)*{\left( {{Latitude}\mspace{14mu} 1} \right).\mspace{20mu} 4}}} \right)\mspace{14mu}{Latitude}\mspace{14mu} 2\mspace{14mu}{radians}} = {\left( \frac{\pi}{180} \right)*{\left( {{Latitude}\mspace{14mu} 2} \right).5}}} \right)\mspace{14mu} a} = {{{\sin\left( \frac{{Latitude}\mspace{14mu}{Difference}}{2} \right)}*{\sin\left( \frac{{Latitude}\mspace{14mu}{Difference}}{2} \right)}} + {{\sin\left( \frac{{Longitude}\mspace{14mu}{Difference}}{2} \right)}*{\sin\left( \frac{{Longitude}\mspace{14mu}{Difference}}{2} \right)}*{\cos\left( {{Latitude}\mspace{14mu} 1\mspace{14mu}{Radians}} \right)}*{{\cos\left( {{Latitude}\mspace{14mu} 2\mspace{14mu}{Radians}} \right)}.\mspace{20mu} 6}}}} \right)\mspace{14mu} c} = {2*{{\arctan\left( \frac{\sqrt{a}}{\sqrt{1 - a}} \right)}.\mspace{20mu} 7}}} \right)\mspace{14mu}{R\left( {{in}\mspace{14mu}{km}} \right)}} = 6371.$  Distance  from  previous  location = R * c.

If the velocity of the electronic device 10 is known, then the previouslocation and the velocity can be used to compare the intersectioncoordinates and determine if either are reliable and/or if one is morereliable than the other. Using the above equations provides the distancefrom the previous location to the current location, so that the distancecan be evaluated to determine if such distance is feasible. If thedistance is too great, then the current location may be disregarded. Ifthe distance is not too great, then the current location is reliable. Indetermining whether the distance is feasible, the velocity of theelectronic device 10 can be evaluated in combination with the previouslocation. One query is whether the current position is possible giventhe known previous location and velocity. For example, if the distancefrom the previous location is calculated one second later and is 500feet away, and the electronic device 10 was traveling 55 mph (about 80feet per second), then the current location is not reliable. However, ifthe distance from the previous location is calculated one second laterand is 75 feet away, and the electronic device 10 was traveling 55 mph(about 80 feet per second), then the current location may be consideredreliable.

The subject invention may also utilize a threshold based on a fixedvelocity or speed when evaluating the distance from the previouslocation. For example, the previous location could be evaluated atspeeds of 5 mph, 10 mph, 15 mph and at the actual speed. If the currentlocation is reliable based on such evaluation, then it is stored andupdated. The threshold could also be dependent upon the actual speed ifknown. For instance, if the electronic device 10 is or was moving at 55mph, then the threshold could be measured in 5 mph intervals, such as at45, 50, 60, 65 mph for the evaluation. Since the measurements areoccurring at a very rapid pace, 10 to 100 times a second, the electronicdevice 10 could only change speed or velocity so much. Therefore, thethreshold may have smaller intervals, such as 1 mph.

Once the intersection is determined to be reliable, the new coordinatesare generated for the electronic device 10 corresponding to the reliableintersection. The new coordinates are stored in the electronic device 10and the location of electronic device 10 is updated.

Additionally, if the first location, velocity and direction of theelectronic device 10 is known, an estimated location can be calculatedbased on this information and a tolerance associated with the estimatedlocation can be established. Depending on the velocity or the desiredaccuracy, the tolerance may be a few inches to a few feet. The estimatedlocation can be compared to the current location to determine if thecurrent location is within the tolerance and storing locations withinthe tolerance. If one of the intersection coordinates are within thetolerance, then this intersection coordinate is reliable and can berecorded as the new coordinate and current location of the electronicdevice 10.

In one particular application, the electronic device 10 may be in motionand, thus, the method includes the step of retrieving a currentdirection of the electronic device 10 and comparing the currentdirection to an initial direction. If the current direction and initialdirection are the same, then the method is restarted. Said differently,in this example, the electronic device 10 has not moved so the methodcontinues to monitor for motion. In order to precisely locate theelectronic device 10 in a field when the electronic device 10 is moving,the current direction of the electronic device 10 is retrieved andcompared to an initial direction to determine whether the currentlocation is within specified boundaries. If the current direction isoutside of the specified boundaries, the method is restarted.

In order to ensure precision and accuracy of the location, the subjectinvention monitors for signals having a higher signal quality thaneither of the first and second signals. The monitoring may beaccomplished by continuously scanning for signals or scanning atpredetermined time intervals. The electronic device 10 may initiate anew search for a new plurality of signals and re-measure signal qualityafter expiration of the predetermined time and selecting the two signalswith the highest signal quality. For example, the first and secondsignals may be used for the predetermined amount of time before theelectronic device 10 checks for a different signal having a highersignal quality. If the first and second signals remain the highestquality, then the location determination continues with these signals.The antenna 24 may also re-tune its configuration to maintain the firstand second signal as the highest quality while the electronic device 10is in motion.

If a new, third signal is detected and it is determined that the signalquality of the third signal from a third transmitting device 12 c havinga third signal type is of a higher quality, then the signal with thelowest signal quality is dropped and the third signal is designated forlocation determination. The determination of the signal quality of thethird signal proceeds in the same manner as described above for thefirst and second signals.

Similarly to the first and second signals discussed above, once thethird signal is selected, the antenna 24 is tuned for the third signaltype and the third signal is received with the tuned antenna 24. Thereceived third signal is then used to determine the distance theelectronic device 10 is from the third transmitting device 12 c asdescribed above for the first and second signals, including developing athird transmission circle, determining points of intersection betweenthe third transmission circle and the remaining one of the first andsecond transmission circles, and determining which of the two points ofintersection is reliable. New coordinates may be generated for theelectronic device 10 based upon the distances from the first and thirdtransmitting devices 12, which are recorded as a current location of theelectronic device 10.

The first location and current location may also be output to a mappingprogram for display to a user. The map can be displayed on a display ofthe electronic device 10. This output may be done continuously or a settime interval. Referring to FIGS. 7A-7D, a graphical display of amapping program is shown having the location of the electronic device 10plotted. In FIG. 7A, the view shown is zoomed out, while FIG. 7B shows acloser view. FIG. 7C shows an even closer view where each of thelocations is visible and FIG. 7D shows that the subject invention isable to detect the location with lane level accuracy. Lane levelaccuracy is able to distinguish the location between adjacent lanes on aroadway. The subject invention is able to determine the location withina few feet and preferably within 3 feet or less.

The electronic device 10 may also communicate with other componentsdepending on the particular application. For example, if the subjectinvention is incorporated into a vehicular application, it maycommunicate with sensors connected to wheels, a motor for driving thewheels, brakes, lights, audio and video equipment, navigation systemequipment, a steering wheel, and other components for controlling thevehicle 40, gathering input from a user (driver) of the vehicle 40, andsupplying output to the user of the vehicle 40. As an example, theelectronic device 10 in a vehicle 40 may ascertain its initial locationusing a GPS signal from the vehicle 40 or the electronic device 10, butmay rely on signal strength measurements from transmitting devices 12 toaccurately identify the location of vehicle 40.

Referring to FIG. 8, an example of a method that can be performed todetermine a location of the electronic device 10 is shown. The methodcan be performed by the processor 30 executing instructions in acomputer program encoded on a tangible program carrier or stored withinthe electronic device 10. For example, some or all of the method can beperformed in the electronic device 10. The electronic device 10 performsthe method every 100 ms. In step 100, the electronic device 10 receivesWi-Fi signals from transmitting devices 12 and submits a location queryto the transmitting devices 12 in step 102 to receive RSSI, power andgain, and/or device information. In step 104, the two highest qualitysignals received are determined and used for location determinationwhich may include signal smoothing and noise reduction relying on thepropagation characteristics of the signals.

The present direction is received from a gyroscope 34 in step 106. Ifthis is the first cycle, then the location and direction are stored, andthe cycle restarts. If this is not the first cycle, then the previouslocation and direction are retrieved in step 108. The previous locationmay be stored in the memory of the electronic device 10. If the previouslocation and direction are the same as the current, then the cycle isrestarted. However, if they are different, then any movement anddirection is retrieved from the gyroscope 34 in step 110. The retrievedmovement and direction are evaluated for accuracy in step 112. Thelocation and direction are evaluated to be within specified boundaries.Specific boundaries may be based on distance traveled, time elapsed,velocity, etc. as discussed above. If the location and direction areoutside of specification, then the location is abandoned and the cycleis restarted in step 114. If it is within specification, then anestimated current location is determined in step 116 based on theprevious location, velocity, and the tolerance is established. In step118, the current location is compared to the estimated current location.If the result is outside of the tolerance, then the location isabandoned and the cycle is restarted in step 120. If the result iswithin the tolerance, then the location is updated and/or reported andthe cycle is restarted in step 122.

Referring to FIGS. 9A and 9B, another example of a method that can beperformed to determine a location of the electronic device 10 is shown.The method can be performed by the processor 30 executing instructionsin a computer program encoded on a tangible program carrier or storedwithin the electronic device 10. For example, some or all of the methodcan be performed in the electronic device 10. FIG. 9A generallydiscloses the steps for determining signal quality from the plurality ofreceived signals and FIG. 9B generally discloses the steps forperforming bilateration to determine the location of the electronicdevice 10.

In FIG. 9A, the electronic device 10 receives multiple types of signalsin step 200. As discussed above, the electronic device 10 may be able todetect and receive many different types of signals. The electronicdevice 10 then determines two signals for evaluation in step 202. Foreach of the signals, in step 204, the signal strength data is gatheredand signal propagation characteristics for the signals are compared tothe signal strength data in step 206. If the signals are of sufficientlyhigh signal quality, then the antenna 24 is tuned for these two signalsin step 208. Next, the bilateration is performed in step in 210. If afailure occurs, then the failure is recorded in step 212.

Referring to FIG. 9B, the bilateration begins by determining thedistance that the electronic device 10 is from the first and secondtransmitting devices 12 in step 214. As described above, the distancecan be determined from the received signal power and gain andtransmitted power and signal gain or location information associatedwith the transmitting device 12. Next, circles are created based on thedistances in step 216 and the coordinates of the intersection of thecircles is determined in step 218. Step 220 is the evaluation of theintersection coordinates to determine if one of the coordinates is morereliable than the other. If one intersection coordinate is morereliable, than the location of the electronic device 10 is updated instep 222. The updated location is recorded as the current location andthe cycle repeats at step 202. In step 224, an indicate failure can be arejection such that a determined location can be rejected upondetermining that a difference in the determined location exceeds athreshold. For example, the electronic device 10 can reject the mostrecently determined location if the location is more than a maximumdistance from the most recently determined location(s). In someimplementations, at least part of a power information for at least oneof the transmitting devices 12 can be removed upon determining that adifference in the detected power for the transmitting device 12 exceedsa threshold. For example, the electronic device 10 can remove the powerinformation for the transmitting device if the signal power is too muchstronger or weaker than the most recently obtained signal power(s).

With reference to FIG. 10, another process diagram for carrying out thesubject invention is shown. When the electronic device 10 starts, itretrieves the first, or previous location in step 300. Next, in step302, the electronic device 10 queries the surrounding transmittingdevices 12 using Wi-Fi and obtains a current location using thetechniques described above. In step 304, the electronic device 10 checksthe gyroscope 34 for any change of position. In step 306, the electronicdevice 10 checks the compass 36 for any magnetic directional change. Anychanges from the gyroscope 34 and compass 36 are compared to theprevious locations in step 308 and evaluated to determine if an updateis newer, more accurate, or more reliable. If this is the first cycle,then steps 300-308 are repeated. In step 310, if the results are equal,the process is terminated. If the results are different, they arestored. In step 312, the electronic device 10 stops listening forupdates and in step 314, an estimated location is determined from thegyroscope 34, compass 36, and current location.

FIGS. 11 and 12 represents a process where the electronic device 10 maynot have a physical accelerometer 38 so that the accelerometer 38function is performed virtually. Referring to FIG. 11, the first step isto retrieve the last reported, or previous, location of the electronicdevice 10 in step 400. This location may be saved in the local memory orthe local database or stored remotely. The current location iscalculated in step 402 using the methods described above. In step 404,the current location is retrieved and stored and in step 406, a distancebetween the previous location and the current location is compared. Instep 408, the distance between locations is stored. Steps 400 through408 continue to repeat at desired intervals. Next, in step 410, thedistance between locations is compared for each cycle of steps 400through 408 and saved as a cycle comparison result in step 412. In step414, if the latest cycle comparison result is different and if it isdetermined accurate in step 416, then the virtual accelerometer 38 isset to 1 and if they are the same, the virtual accelerometer 38 is setto 0. In some implementations, determined location(s) can be compared toa predetermined number of locations determined previously. FIG. 11 is analternative virtual accelerometer 38 based on changes of locations onlyand not based on multiple cycles as shown in FIG. 10. In step 500, thepresent location of the electronic device 10 is calculated as describedabove. The present location is compared with a previous location in step502, and the difference is calculated in step 504, and stored in step506. If there is a difference, then the virtual accelerometer 38 is setto 1 in step 508. If there is no difference, then the virtualaccelerometer 38 is set to 0 in step 510.

Some or all steps of the method can be omitted in some implementations.In some implementations, one or more additional steps can be performed.One or more steps can be repeated, performed earlier or later, and/orperformed in a different order, to name just a few examples.

The disclosed and other embodiments and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of one or more of them. The disclosedand other embodiments can be implemented as one or more computer programproducts, i.e., one or more modules of computer program instructionsencoded on a computer-readable medium for execution by, or to controlthe operation of, data processing apparatus. The computer-readablemedium can be a machine-readable storage device, a machine-readablestorage substrate, a memory device, or a combination of one or morethem. The term “data processing apparatus” encompasses all apparatus,devices, and machines for processing data, including by way of example aprogrammable processor 30, a computer, or multiple processors 30 orcomputers. The apparatus can include, in addition to hardware, code thatcreates an execution environment for the computer program in question,e.g., code that constitutes processor firmware, a protocol stack, adatabase management system, an operating system, or a combination of oneor more of them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub-programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output as would be understood by those of ordinary skill inthis art. The processes and logic flows can also be performed by, andapparatus can also be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors 30 suitable for the execution of a computer program include,by way of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor 30 will receive instructions and data from a read-only memoryor a random access memory or both. The essential elements of a computerare a processor 30 for performing instructions and one or more memorydevices for storing instructions and data. Generally, a computer willalso include, or be operatively coupled to receive data from or transferdata to, or both, one or more mass storage devices for storing data,e.g., magnetic, magneto-optical disks, or optical disks. However, acomputer need not have such devices. Computer-readable media suitablefor storing computer program instructions and data include all forms ofnon-volatile memory, media and memory devices, including by way ofexample semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory devices; magnetic disks, e.g., internal hard disks or removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor 30 and the memory can be supplemented by, or incorporated in,special purpose logic circuitry.

The disclosed embodiments can be implemented in a system that includes aback-end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation of what is disclosed here, or any combination of one ormore such back-end, middleware, or front-end components. The componentsof the system can be interconnected by any form or medium of digitaldata communication, e.g., a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), e.g., the Internet.

The system can include clients and servers. A client and server aregenerally remote from each other and typically interact through acommunication network. The relationship of client and server arises byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of the claims or of what may beclaimed, but rather as descriptions of features specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understand as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments, and it should beunderstood that the described program components and systems cangenerally be integrated together in a single software product orpackaged into multiple software products.

Particular embodiments of the subject matter described in thisspecification have been described. Other embodiments are within thescope of the following claims. For example, the actions recited in theclaims can be performed in a different order and still achieve desirableresults. As one example, the processes depicted in the accompanyingfigures do not necessarily require the particular order shown, orsequential order, to achieve desirable results. In certainimplementations, multitasking and parallel processing may beadvantageous. It will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims

What is claimed is:
 1. A method of navigating a vehicle with anelectronic device using bilateration to a desired location, said methodcomprising the steps of: receiving, with the electronic device, aplurality of signals emitted from a plurality of transmitting deviceswithin a vicinity of the electronic device; determining a signal qualityfor the plurality of signals that are received based on: 1) a receivedsignal strength indicator or 2) a received signal power and a receivedsignal gain, and signal propagation characteristics based ontransmitting device information that comprises manufacturer and type oftransmitting device for each of the plurality of transmitting devices;comparing the signal propagation characteristics with either 1) thereceived signal strength indicator or 2) the received signal power andthe received signal gain and designating at least two of the pluralityof signals having highest signal quality for location determination;determining a distance that the electronic device is from thetransmitting devices using the two highest signal quality signals forlocating the electronic device; and generating new coordinates for theelectronic device based upon the distances from the plurality oftransmitting devices and recording the new coordinates as a currentlocation of the electronic device to thereby navigate the vehicle; andcomparing the current location of the vehicle to the desired locationand continuing to generate new coordinates as the vehicle moves.
 2. Themethod as set forth in claim 1 further comprising the step of retrievinga current direction of the vehicle through the electronic device andcomparing the current direction to an initial direction and restartingsaid method in response to the current direction and the initialdirection being the same.
 3. The method as set forth in claim 1 furthercomprising the step of retrieving a current direction of the vehiclethrough the electronic device and comparing the current direction to aninitial direction and determining whether the current location is withinspecified boundaries.
 4. The method as set forth in claim 3 furthercomprising the step of restarting said method in response to the currentdirection being outside of the specified boundaries.
 5. The method asset forth in claim 1 further comprising the step of calculating anestimated location based on a previous location, velocity and directionof the vehicle through using electronic device, and establishing atolerance associated with the estimated location.
 6. The method as setforth in claim 5 wherein the velocity and direction are provided by atleast one or more of an accelerometer or a gyroscope.
 7. The method asset forth in claim 5 further comprising the step of comparing theestimated location to the current location to determine if the currentlocation is within the tolerance and storing locations within thetolerance.
 8. The method as set forth in claim 5 wherein the step ofgenerating new coordinates further comprises the steps of developingfirst and second transmission circles based upon the distances from thetransmitting devices and signal propagation characteristics; determiningpoints of intersection where the first and second transmission circlesintersect; determining which of the two points of intersection isreliable; and generating new coordinates for the electronic device basedupon the reliable intersection.
 9. The method as set forth in claim 8further comprising the step of determining if the current location iswithin the tolerance and if one of the intersection coordinates arewithin the tolerance, then this intersection coordinate is deemedreliable.
 10. The method as set forth in claim 9 wherein the step ofdetermining which of the two points of intersection are reliable isfurther defined as comparing the points of intersection with the currentand desired locations relative to the velocity and direction inputs anddetermine which of the points is feasible.
 11. The method as set forthin claim 10 further comprising updating transmission circles based uponchanges to the signal propagation characteristics for each signalmeasured.
 12. The method as set forth in claim 11 where the step ofupdating the transmission circles occurs at least 10 times per second.